Technical Field
The present invention relates to an optical scanning apparatus and an image display apparatus.
Background Art
Image display apparatuses such as head up displays (HUD) are disposed to transportation vehicles such as automobiles, airplanes, and ships. The HUD can generate an intermediate image, and project and display the generated intermediate image on a windshield to provide information to an operator such as a driver.
The HUD can employ a panel system and a laser scanning system as a projection system of the intermediate image. As to the panel system, an imaging device such as a liquid crystal device and a digital mirror device projects the intermediate image. As to the laser scanning system, a light source unit including a laser diode (light emitter) emits a laser beam, and then a two dimensional scanning device scans a target scan surface by using the laser beam to project the intermediate image. As to the panel system, an image is formed by partially blocking the light from the light emitters by using the imaging device. As to the laser scanning system, an image is formed by controlling the light emission of the light emitters pixel by pixel, and thereby a high contrast image can be formed.
As to the head up display (HUD) using the laser scanning system, image visibility can be increased by adjusting the light emission luminance of an image based on brightness of background of the displayed image. However, if the dynamic range of the light source such as a laser diode is not sufficient, image quality may deteriorate.
Further, as to the head up display (HUD) employing the laser scanning system, it is required to acquire a control signal to control an emission timing of the laser diode to generate an image at a desired position. Typically, the control signal can be generated by receiving the light, emitted from the laser diode and used for the scanning, by a light receiving element.
However, as described above, if the light quantity of the light that irradiates the target scan surface becomes too little, the light quantity of the light received by the light receiving element becomes lower, with which the control signal used for controlling the emission timing of the laser diode cannot be acquired, with which image quality is degraded.